1. Field of the Invention
The invention relates to an antenna diversity method for a wireless network adapter.
2. Description of the Related Art
In a wireless local area network (WLAN), the antenna diversity of a wireless network adapter conventionally utilizes the method of packet-by-packet signal intensity comparison. FIG. 1 is a flowchart showing a conventional antenna diversity method of a packet-by-packet signal intensity comparison. As shown in FIG. 1, when the wireless network adapter has detected that a packet is inputted, the signal intensity of this antenna (e.g. antenna A) will be judged first, and then the operating antenna is switched to another antenna (e.g. antenna B). Thereafter, the wireless network adapter compares the signal intensities of the two antennas, and the operating antenna is switched to the antenna with the larger intensity. Therefore, each time when the packet enters, the wireless network adapter repeats this step. When the system wants to transmit the packet, the packet is transmitted through the selected antenna.
Although this diversity method of packet-by-packet detection has better performance under the condition of serious signal's fast fading, switching the antenna may cause serious DC offset when the radio frequency (RF) architecture is under the direct conversion. Thus, the precise value of measuring the received signal intensity after the switching cannot be obtained until the DC offset disappears. However, if the time length of preamble signal is quite short (for example, 8 μs in the IEEE 802.11 a/g condition), there is not enough time to measure the received signal intensity after the DC offset disappears.
Consequently, the diversity method of packet-by-packet detection encounters the above-mentioned problem when the time length of preamble signal is short and the radio frequency adopts the direct conversion architecture.